While only one-quarter of all travel occurs at night, about half of the traffic fatalities occur during nighttime hours. To address this disparity and promote highway safety, the Federal Highway Administration (FHWA) has adopted traffic sign retroreflectivity requirements. Regulations contained in the Manual of Uniform Traffic Control Devices (MUTCD) include a standard for minimum levels of retroreflectivity that must be maintained for traffic signs. The regulation applies to most regulatory, warning, street name, ground-mounted and overhead guide signs, whether permanent, temporary or portable, on all public roads and private property where the public is invited to travel.
In order to maintain traffic sign retroreflectivity at or above the minimum levels, it is necessary to have a device with which to measure the retroreflectivity levels of the sheeting, or possess a visual reference standard that can be compared against the traffic sign. As one method of determining that signs are at or above the minimum levels, the FHWA recommends that all agencies conduct nighttime visual assessments of individual traffic signs within their jurisdiction. The process requires a sign inspector to view a sign at a known retroreflective level which is at the minimum level defined by the standard to establish the evaluation threshold for that night's inspection activities. Agencies typically may find such signs by looking through their inventory of old or discarded signs (if available). However, without equipment to measure the retroreflectivity of these old or discarded signs, the agency does not know if their discarded sign is an accurate representation of the minimum standard. Most agencies do not possess devices to measure retroreflectivity. Portable retroreflectometers typically are priced beyond the maintenance budgets of many city, county, village and townships that are responsible for maintaining the signs. Further, the devices themselves are not well suited to the rigors of being constantly used in the field by maintenance crews, thereby requiring ongoing maintenance and periodic calibration to accurately measure retroreflectivity.
When nighttime visual sign inspections result in the identification of signs which may have marginal retroreflectivity (i.e., the signs are determined by the inspector to not clearly be above the minimum retroreflectivity), an agency requires the means to determine if the sign is above, or below the minimum standard. If an agency possesses a portable retroreflectometer, a measurement can be conducted, and a decision regarding the continued effectiveness (and use) of the sign can be made. As an alternate procedure, an inspector may attach smaller panels cut from older signs that are at the minimum retroreflectivity levels to the sign in question, and conduct a comparative review under retroreflected light. However, without a retroreflectometer to measure sign retroreflectivity, the inspector cannot be certain that the smaller panel is at the required minimum retroreflectivity level or is an accurate visual representation of the minimum standard.
Thus, it would be desirable to provide a plurality of retroreflective sheeting, having various colors and retroreflectivity levels that are known and/or certified to be at the minimum retroreflectivities required by the MUTCD standard. These and other advantages may be provided by one or more embodiments of the present invention.